1. Field of the Invention
The present invention relates to a wireless communication system that supports at least one of SC-FDMA, MC-FDMA, and OFDMA, and more particularly, to a method for resolving collision of signals transmitted in uplink in the wireless communication system.
2. Discussion of the Related Art
An E-UMTS system is an evolved version of the WCDMA UMTS system and basic standardization thereof is in progress under the 3rd Generation Partnership Project (3GPP). The E-UMTS is also referred to as a Long Term Evolution (LTE) system. For details of the technical specifications of the UMTS and E-UMTS, refer to Release 7 and Release 8 of “3rd Generation Partnership Project; Technical Specification Group Radio Access Network”.
The E-UMTS mainly includes a User Equipment (UE), base stations (or eNBs or eNode Bs), and an Access Gateway (AG) which is located at an end of a network (E-UTRAN) and which is connected to an external network. Generally, an eNB can simultaneously transmit multiple data streams for a broadcast service, a multicast service and/or a unicast service. The AG can be divided into a part that handles processing of user traffic and a part that handles control traffic. Here, the AG part for processing new user traffic and the AG part for processing control traffic can communicate with each other using a new interface. One or more cells may be present for one eNB. An interface for transmitting user traffic or control traffic can be used between eNBs. A Core Network (CN) may include the AG and a network node or the like for user registration of UEs. An interface for discriminating between the E-UTRAN and the CN can be used. The AG manages mobility of a UE on a Tracking Area (TA) basis. One TA includes a plurality of cells. When the UE has moved from a specific TA to another TA, the UE notifies the AG that the TA where the UE is located has been changed.
FIG. 1 illustrates a network structure of an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) system. The E-UTRAN system is an evolved version of the conventional UTRAN system. The E-UTRAN includes base stations that will also be referred to as “eNode Bs” or “eNBs”. The eNBs are connected through X2 interfaces. The X2 user plane interface (X2-U) is defined between eNBs. The X2-U interface provides non guaranteed delivery of user plane PDUs. The X2 control plane interface (X2-CP) is defined between two neighbour eNBs. The X2-CP performes following functions: context transfer between eNBs, control of user plane tunnels between source eNB and target eNB, transfer of handover related messages, uplink load management and the like. Each eNB is connected to User Equipments (UEs) through a radio interface and is connected to an Evolved Packet Core (EPC) through an S1 interface. The S1 user plane interface (S1-U) is defined between the eNB and the S-GW. The S1-U interface provides non guaranteed delivery of user plane PDUs between the eNB and the S-GW (Serving Gateway). The S1 control plane interface (S1-ME) is defined between the eNB and the MME (Mobility Management Entity). The S1 interface performes following functions: EPS (Enhanced Packet System) Bearer Service Management function, NAS (Non-Access Stratum) Signalling Transport function, Network Sharing Function, MME Load balancing Function and the like.
FIG. 2 illustrates the configurations of a control plane and a user plane of a radio interface protocol between the E-UTRAN and a UE based on the 3GPP radio access network standard. The radio interface protocol is divided horizontally into a physical layer, a data link layer, and a network layer, and vertically into a user plane for data transmission and a control plane for signaling. The protocol layers of FIG. 2 can be divided into an L1 layer (first layer), an L2 layer (second layer), and an L3 layer (third layer) based on the lower three layers of the Open System Interconnection (OSI) reference model widely known in communication systems.
The control plane is a passage through which control messages that a UE and a network use in order to manage calls are transmitted. The user plane is a passage through which data (e.g., voice data or Internet packet data) generated at an application layer is transmitted. The following is a detailed description of the layers of the control and user planes in a radio interface protocol.
The physical layer, which is the first layer, provides an information transfer service to an upper layer using a physical channel. The physical layer is connected to a Media Access Control (MAC) layer, located above the physical layer, through a transport channel. Data is transferred between the MAC layer and the physical layer through the transport channel. Data transfer between different physical layers, specifically between the respective physical layers of transmitting and receiving sides, is performed through the physical channel. The physical channel is modulated according to the Orthogonal Frequency Division Multiplexing (OFDM) method, using time and frequencies as radio resources.
The MAC layer of the second layer provides a service to a Radio Link Control (RLC) layer, located above the MAC layer, through a logical channel. The RLC layer of the second layer supports reliable data transmission. The functions of the RLC layer may also be implemented through internal functional blocks of the MAC layer. In this case, the RLC layer need not be present. A PDCP layer of the second layer performs a header compression function to reduce unnecessary control information in order to efficiently transmit IP packets such as IPv4 or IPv6 packets in a radio interface with a relatively narrow bandwidth.
A Radio Resource Control (RRC) layer located at the bottom of the third layer is defined only in the control plane and is responsible for control of logical, transport, and physical channels in association with configuration, re-configuration, and release of Radio Bearers (RBs). The RB is a service that the second layer provides for data communication between the UE and the E-UTRAN. To accomplish this, the RRC layer of the UE and the RRC layer of the network exchange RRC messages. The UE is in an RRC connected mode if an RRC connection has been established between the RRC layer of the radio network and the RRC layer of the UE. Otherwise, the UE is in an RRC idle mode.
A Non-Access Stratum (NAS) layer located above the RRC layer performs functions such as session management and mobility management.
One cell of the eNB is set to use a bandwidth such as 1.25, 2.5, 5, 10 or 20 MHz to provide a downlink or uplink transmission service to UEs. Here, different cells may be set to use different bandwidths.
Downlink transport channels for transmission of data from the network to the UE include a Broadcast Channel (BCH) for transmission of system information, a Paging Channel (PCH) for transmission of paging messages, and a downlink Shared Channel (SCH) for transmission of user traffic or control messages. User traffic or control messages of a downlink multicast or broadcast service may be transmitted through a downlink SCH and may also be transmitted through a downlink multicast channel (MCH). Uplink transport channels for transmission of data from the UE to the network include a Random Access Channel (RACH) for transmission of initial control messages and an uplink SCH for transmission of user traffic or control messages.
Logical channels, which are located above the transport channels and are mapped to the transport channels, include a Broadcast Control Channel (BCCH), a Paging Control Channel (PCCH), a Common Control Channel (CCCH), a Multicast Control Channel (MCCH), and a Multicast Traffic Channel (MTCH).
FIG. 3 illustrates an example of a physical channel structure used in an E-UMTS system. A physical channel includes a plurality of subframes in the time axis and a plurality of subcarriers in the frequency axis. Here, one subframe includes a plurality of symbols in the time axis. One subframe includes a plurality of resource blocks and one resource block includes a plurality of symbols and a plurality of subcarriers. In addition, each subframe may use certain subcarriers of certain symbols (e.g., a first symbol) of a subframe for a physical downlink control channel (PDCCH), that is, an L1/L2 control channel. An L1/L2 control information transmission region (PDCCH) and a data transmission region (PDSCH) are shown in FIG. 3. The Evolved Universal Mobile Telecommunications System (E-UMTS), which is currently under discussion, uses 10 ms radio frames, each including 10 subframes. Each subframe includes two consecutive slots, each of which is 0.5 ms long. One subframe includes multiple OFDM symbols. Some (for example, the first symbol) of the OFDM symbols can be used to transmit L1/L2 control information. A Transmission Time Interval (TTI), which is a unit time during which data is transmitted, is 1 ms.
The eNB and the UE transmit and receive most data other than a specific control information or specific service data through a PDSCH, which is a physical channel, using a DL-SCH which is a transport channel. Information indicating a UE (one or a plurality of UEs) to which PDSCH data is transmitted and indicating how the UEs receive and decode PDSCH data is transmitted through the PDCCH.
For example, let us assume that a specific PDCCH has been CRC-masked with a Radio Network Temporary Identity (RNTI) “A” and information associated with data transmitted using transport format information (e.g., transport block size, modulation, coding information, etc) “C” and a radio resource (e.g., a frequency position) “B” is transmitted through a specific subframe. Under this assumption, if one or more specific UEs contain the RNTI “A” among UEs in a cell which are monitoring the PDCCH using RNTI information contained in the UEs, the specific UEs receive the PDCCH and receive a PDSCH indicated by “B” and “C” through the received PDCCH information. That is, the PDCCH transmits downlink scheduling information of a specific UE and the PDSCH transmits downlink data corresponding to the downlink scheduling information. The PDCCH can also transmit uplink scheduling information of a specific UE.
FIG. 4 is a block diagram of a transmitter according to a Single Carrier-Frequency Division Multiple Access (SC-FDMA) scheme.
As shown in FIG. 4, the SC-FDMA transmitter includes a DFT unit 410 that performs Discrete Fourier Transform (DFT), a subcarrier mapper 420, and an IFFT unit 430 that performs Inverse Fast Fourier Transform (IFFT).
The DFT unit 410 performs DFT on received time-domain data and outputs frequency-domain symbols. The subcarrier mapper 420 maps frequency-domain symbols to subcarriers. The IFFT unit 430 performs IFFT on received frequency-domain symbols and outputs a time-domain signal
FIG. 5 illustrates a structure of a radio frame used for uplink transmission.
As shown in FIG. 5, one radio frame includes 10 subframes and each subframe includes 2 slots. The time required to transmit one subframe is referred to as a “Transmission Time Interval (TTI)”. For example, the length of each subframe may be 1 ms and the length of each slot may be 0.5 ms. One slot includes a plurality of SC-FDMA symbols in the time domain and includes a plurality of resource blocks in the frequency domain. This radio frame structure is only illustrative and the number of subframes included in a radio frame, the number of slots included in a subframe, or the number of SC-FDMA symbols included in a slot may vary.
FIG. 6 illustrates a resource grid of an uplink slot.
As shown in FIG. 6, one uplink slot includes a plurality of SC-FDMA symbols in the time domain and includes a plurality of resource blocks in the frequency domain. Although one uplink slot includes 7 SC-FDMA symbols and one resource block includes 12 subcarriers in the example of FIG. 6, this structure is only illustrative. For example, the number of SC-FDMA symbols included in one uplink slot may be changed according to the length of a Cyclic Prefix (CP).
Each element in the resource grid is referred to as a resource element. One resource block includes 12×7 resource elements. The number of resource blocks (NUL) included in one uplink slot depends on an uplink transmission bandwidth set in the cell.
FIG. 7 illustrates a structure of an uplink subframe to which SC-FDMA is applied.
As shown in FIG. 7, an uplink subframe can be divided into a region to which a Physical Uplink Control Channel (PUCCH) carrying uplink control information is allocated and a region to which a Physical Uplink Shared Channel (PUSCH) carrying user data is allocated. A middle portion of the subframe is allocated to the PUSCH and both side portions of a data region in the frequency domain are allocated to the PUCCH. The UE does not simultaneously transmit the PUCCH and the PUSCH.
Uplink control information transmitted in the PUCCH includes an Acknowledgement (ACK)/Negative-Acknowledgement (NACK) signal used to perform Hybrid Automatic Repeat Request (HARQ), a Channel Quality Indicator (CQI) indicating a downlink channel status, and a scheduling request signal which serves to request allocation of uplink radio resources. As an exception, if a PUSCH transmission is present while the uplink control information is transmitted, the UE transmits the uplink control information using the PUSCH.
A PUCCH for one UE uses one resource block that occupies a different frequency in each of the two slots in one subframe. The two slots use different resource blocks (or subcarriers) in the subframe. That is, the two resource blocks allocated to PUCCHs are subjected to frequency hopping in the slot boundary. In the example illustrated in FIG. 7, a PUCCH of m=0, a PUCCH of m=1, a PUCCH of m=2, and a PUCCH of m=3 (PUCCHs for 4 UEs) are allocated to a subframe.
The PUCCH can support multiple formats. That is, the PUCCH can transmit uplink control information having a different number of bits per subframe depending on the modulation scheme. For example, 1-bit uplink control information can be transmitted through the PUCCH when Binary Phase Shift Keying (BPSK) is used and 2-bit uplink control information can be transmitted through the PUCCH when Quadrature Phase Shift Keying (QPSK) is used.
FIG. 8 illustrates a random access procedure.
The random access procedure is used to transmit short-length data in uplink. For example, the random access procedure is performed upon initial access in an RRC idle mode, upon initial access after radio link failure, upon handover requiring the random access procedure, and upon the occurrence of uplink/downlink data requiring the random access procedure during an RRC connected mode. Some RRC messages such as an RRC connection request message, a cell update message, and a URA update message are transmitted using a random access procedure. Logical channels such as a Common Control Channel (CCCH), a Dedicated Control Channel (DCCH), or a Dedicated Traffic Channel (DTCH) can be mapped to a transport channel (RACH). The transport channel (RACH) can be mapped to a physical channel (e.g., Physical Random Access Channel (PRACH)). When a UE MAC layer instructs a UE physical layer to transmit a PRACH, the UE physical layer first selects an access slot and a signature and transmits a PRACH preamble in uplink. The random access procedure is divided into a contention-based procedure and a non-contention-based procedure.
As shown in FIG. 8, a UE receives and stores information regarding random access from an eNB through system information. Thereafter, when random access is needed, the UE transmits a random access preamble (Message 1) to the eNB (S810). Upon receiving the random access preamble from the UE, the eNB transmits a random access response message (Message 2) to the UE (S820). Specifically, downlink scheduling information for the random access response message can be CRC-masked with a Random Access-RNTI and can be transmitted through an L1/L2 control channel (PDSCH). Upon receiving the downlink scheduling signal masked with the RA-RNTI, the UE can receive and decode a random access response message from a Physical Downlink Shared Channel (PDSCH). Thereafter, the UE checks whether or not random access response information corresponding to the UE is present in the received random access response message. Whether or not random access response information corresponding to the UE is present can be determined based on whether or not a Random Access preamble ID (RAID) for the preamble that the UE has transmitted is present. The random access response information includes Timing Advance (TA) indicating timing offset information for synchronization, information of allocation of radio resources used in uplink, and a temporary identity (e.g., T-CRNTI) for user identification. Upon receiving the random access response information, the UE transmits an uplink message (Message 3) through an uplink Shared Channel (SCH) according to radio resource allocation information included in the response information (S830). After receiving the uplink message from the UE, the eNB transmits a contention resolution message (Message 4) to the UE (S840).
As in the 3GPP LTE system, uplink packets in a cellular radio packet transmission system which uses the SC-FDMA scheme for uplink transmission are discriminated as they use different time-frequency resources. In the case where an SC-FDMA UE transmits a signal using two or more frequency regions that are not adjacent in the frequency axis at the same time (or the same subframe), single-carrier characteristics of the SC-FDMA are degraded and thus it is necessary to increase the dynamic range of a transmission amplifier of the UE. Accordingly, in order to maintain the single-carrier characteristics of the SC-FDMA, it is preferable that the UE transmit a signal using subcarriers that are adjacent in the frequency axis. In the Time Division Multiple Access (TDMA) system, it may also be undesirable to allow one UE to simultaneously transmit two or more packets with different characteristics for a variety of technical reasons.